激光退火工艺对化学沉积Ni-Mo-P镀层组织及硬度的影响

Effects of Laser Annealing Processes on Microstructure and Hardness of Electroless Ni-Mo-P Coating

目的研究两种激光退火工艺（线光斑无搭接扫描、圆光斑搭接扫描）对非晶态结构的Ni-4.6Mo-12.4P镀层晶化组织特征及硬度的影响。方法在Q235钢基体上化学沉积Ni-Mo-P镀层,然后用两种激光工艺对其进行热处理。通过XRD测试并结合Jade软件定量分析镀层晶化程度、结晶相质量分数及其晶粒尺寸,利用SEM/EDS确定镀层的成分及表面形貌,采用纳米压痕技术对镀层进行硬度测试,最后对两种激光工艺进行对比。结果 Ni-Mo-P镀层在线光斑扫描速度低于12 mm/s、圆光斑扫描速度低于10 mm/s时,发生Ni_3P晶化反应,同时伴有Ni-Mo固溶体形成。Ni_3P相的晶粒尺寸大于Ni/Ni-Mo相尺寸,但扫描速度为6 mm/s时,Ni/Ni-Mo相尺寸大于Ni_3P相尺寸。扫描速度相同时,线光斑扫描镀层比圆光斑扫描镀层获得更高的晶化程度和Ni_3P质量分数,而线光斑扫描的Ni_3P相尺寸小于圆光斑扫描的尺寸。扫描速度为6～10 mm/s时,除扫描速度10 mm/s外,线光斑扫描镀层的硬度较高。结论能量密度高的线光斑无搭接扫描比能量密度低的圆光斑搭接扫描更有利于Ni_3P相的析出,而圆光斑搭接扫描易于Ni_3P相尺寸的长大。镀层的硬度主要受Ni_3P相的尺寸及其质量分数的影响。

The work aims to study the effects of two kinds of laser annealing processes（line spot without overlapping scanning and round spot with overlapping scanning） on microstructural characteristics and hardness of the amorphous Ni-4.6Mo-12.4P（wt.%） coating. The electroless Ni-Mo-P coating was prepared on Q235 steel substrate, and then the coating was laser-annealed by taking advantage of two laser technologies. Crystallization degree, mass fractions of crystalline phase and grain sizes of the coatings were quantitatively analyzed by means of XRD test and Jade software, compositions and morphologies of coatings were determined by SEM/EDS measurement analyses. Hardness of coatings was tested by nanoindentation technology. Finally, two kinds of laser annealing technologies were compared. Accompanied with the formation of Ni-Mo solid solution, crystallization reaction of Ni_3P phase occurred at a line light spot scanning velocity of less than 12 mm/s and a round light spot scanning velocity of less than 10 mm/s. Grain size in Ni_3P phase was larger than that in Ni/Ni-Mo phase. However, the size in Ni/Ni-Mo phase was larger than that in Ni_3P phase at a scanning velocity of 6 mm/s. Higher degree of crystallization and larger mass fraction of Ni_3P phase were obtained on the coating of line light spot scanning than that of the round light spot scanning at the same scanning velocity. But the size in Ni_3P phase with the line light spot scanning was less than that of the round light spot scanning. The hardness of line light spot scanning coating was higher at the scanning velocity of 6 mm/s to 10 mm/s, 10 mm/s was an exception. The line light spot of higher energy density without overlapping scanning is more beneficial to the precipitation of Ni_3P phase than the round light spot of low energy density with overlapping scanning. However, the round light spot with overlapping scanning is beneficial to the growth of Ni_3P phase. Hardness of the coating is mainly influenced by the size and mass fraction of Ni_3P phase.